1. Technical Field
The present invention relates to a scanning unit of an optical position measuring arrangement, by which a scale, which can be moved in relation to it in the scanning direction, can be optically scanned, as well as to a position measuring arrangement having this scanning unit.
2. Background Information
Such scanning units and position measuring arrangements are designed in the form of linear measuring devices having a linear scale, or as rotary measuring devices, having a disk-shaped or drum-shaped scale. They are in particular employed in processing machinery for measuring the relative movement of a tool with respect to a workpiece to be worked, in connection with robots, coordinate measuring machinery, and increasingly in the semiconductor industry.
In many applications, the position measuring arrangement is exposed to electrical fields, in particular to interfering electrical alternating fields, which have an effect on electrically conducting elements of the scanning device and cause electrical interferences and a resultant erroneous position detection.
It is proposed in DE 44 02 554 A1 to shield the detector arrangement against electromagnetic interference fields by a transparent, electrically conducting shielding body, which is connected to ground potential.
In actual use it has been shown that in connection with this construction the production of the shielding device and the electrical contact with ground potential is difficult.